东天山地区中天山地块早二叠世后碰撞伸展与壳幔岩浆作用:来自二长闪长玢岩的制约  

Early Permian Post⁃Collisional Extension and Crust⁃Mantle Magmatism in the Central Tianshan Block,Eastern Tianshan:Constraints from the Study of Porphyritic Monzodiorite

作　　者：张维峰[1,2] 邓新[1] 张利国[1] 王晶[1] 谢国刚[1] 金鑫镖 Zhang Weifeng;Deng Xin;Zhang Liguo;Wang Jing;Xie Guogang;Jin Xinbiao(Wuhan Center of Geological Survey,Wuhan 430205,China;Research Center for Petrogenesis and Mineralization of Granitoids,Wuhan 430205,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国地质调查局花岗岩成岩成矿地质研究中心,湖北武汉430205

出　　处：《地球科学》2024年第8期2697-2713,共17页Earth Science

基　　金：自然科学基金项目(No.41702099);中国地质调查局项目(Nos.DD20221634,DD20190050,DD20190374)。

摘　　要：研究区的二长闪长玢岩出露于中天山地块南缘,是东天山地区二叠纪岩浆活动的典型代表.锆石LA-ICP-MS年代学研究获得其成岩年龄为281.3±1.5 Ma.岩体Na2O+K2O含量和A/CNK分别介于5.88%~6.62%和0.79~0.80之间,显示出高钾钙碱性和准铝质特征.二长闪长玢岩具有高的Fe2O3/FeO比值(0.66~0.73),基质中出现榍石—磁铁矿—石英组合,暗示它们形成于高氧逸度环境下.岩石样品富集大离子亲石元素Rb、K和Ba,而亏损高场强元素Nb、Ta、Ti和重稀土元素.此外,样品的εNd(t)和ISr值分别集中于—2.72~—3.07和0.706 46~0.706 54之间,锆石的εHf(t)值变化于—3.7~—0.8,Nb/U比值变化于10.3~10.9,表明它们来源于交代的石榴石—尖晶石二辉橄榄岩并混合有少量壳源组分.综合考虑中天山地块岩石成因及其他地质资料,我们认为东天山地区的中天山地块在早二叠世处于俯冲板片断裂的后碰撞伸展体系.As a typical case of the Permian magmatism in the Eastern Tianshan,the porphyritic monzodiorite exposed in the southern margin of the Central Tianshan block.Zircon U-Pb dating on the monzodiorite yields an age of 281.3±1.5 Ma.The monzodiorite shows high-K calc-alkaline and metaluminous affinities,with Na2O+K2O and A/CNK values ranging 5.88‒6.62 wt.%and 0.66‒0.73,respectively.They are characterized by high Fe2O3/FeO ratios(0.66~0.73),and present the assemblage of titanite+quartz+magnetite in the groundmass,suggesting that the monzodiorite formed under a high oxygen fugacity condition.The monzodiorite enriched in LILEs(i.e.Rb,K and Ba),but depleted in HFSEs(i.e.Nb,Ta and Ti)and HREE.In addition,all the study samples have negative εNd(t) (−2.72 to −3.07), high initial 87Sr/86Sr (0.706 46 to 0.706 54) values, and negative zircon εHf(t) (− 3.7 to − 0.8) values, as well as intermediate Nb/U (10.3 to 10.9) values. These geochemical features indicating that the magmas originated from spinel - garnet lherzolite that metasomatized by subduction - related fluids, and mixed with minor crustal components. Integrating the petrogenesis and other geological evidences, we proposed that the magmatisms in the Central Tianshan block were generated in post-collision extensional setting of slab breakoff during the Early Permian.

关 键 词：后碰撞伸展 板片断裂 二叠纪 岩石成因 中天山 地球化学 

分 类 号：P581[天文地球—岩石学] P597.3[天文地球—地质学]